1. Field of the Invention
Embodiments of the present invention generally relate to an apparatus and method for detecting substrate breakage and misalignment of a moving substrate in a continuous and cost-effective manner.
2. Description of the Related Art
Substrate processing systems are used to process substrates such as silicon wafers in the production of integrated circuit devices and glass panels in the manufacture of flat panel displays. Typically, one or more robots are disposed in the substrate processing system to transfer substrates through a plurality of process chambers for conducting a sequence of processing steps of the fabrication process. Generally, a substrate processing system includes a cluster tool having a centrally located transfer chamber, with a transfer chamber robot disposed therein, and a plurality of process chambers surrounding the transfer chamber. The transfer chamber is sometimes coupled to a factory interface that houses a factory interface robot and a plurality of substrate cassettes, each of which holds a plurality of substrates. To facilitate substrate transfer between a generally ambient environment within the factory interface and a vacuum environment within the transfer chamber, a load lock chamber which may be pumped down to create a vacuum therein, and vented to provide an ambient condition therein, is disposed between the factory interface and the transfer chamber. The use of robots in the processing of substrates is essential to processing a large number of substrates through many different types of processing technologies with minimal contamination (e.g., substrate handling contamination), high speed, and accuracy to minimize defects and provide a high throughput system.
In operation, the factory interface robot transfers one or more substrates from a cassette to the interior of the load lock chamber. The load lock chamber is pumped down to create a vacuum therein, and then the transfer chamber robot transfers the substrate(s) from the load lock to the interior of one or more of the process chambers. After the substrate processing sequence is completed, the transfer chamber robot returns the processed substrate to the load lock, the load lock is then vented and the factory interface robot transfers the processed substrate to a cassette for subsequent removal from the processing system. Such substrate processing systems are available from AKT, Inc., a wholly-owned subsidiary of Applied Materials, Inc., of Santa Clara, Calif.
The trend towards increasingly larger substrates and smaller device features requires increasingly precise positional accuracy of the substrate in the various process chambers in order to ensure repetitive device fabrication with low defect rates. Increasing the positional accuracy of substrates throughout the processing system is a challenge. In one example, flat-panel display substrates (e.g., glass substrates) are transferred on an end effector (e.g., a blade or fingers) of a robot to and from the various chambers of the processing system. It is difficult to ensure that flat-panel display substrates align properly with the end effectors of the robots, and once aligned, that the substrate can pass through slots or other obstacles in the load lock or process chambers without collisions due to a shift in alignment (i.e., misalignment) during transfer. A collision may not only chip or crack the flat-panel display substrate, but also create and deposit debris in the load lock or process chambers. Creating such debris may result in processing defects or other damage to the display or subsequently processed displays. Thus, the presence of debris often requires shutting down the system, or a portion thereof, to thoroughly remove the potentially contaminating debris. Moreover, with larger dimension substrates and increased device density, the value of each substrate has greatly increased. Accordingly, damage to the substrate or yield loss because of substrate misalignment is highly undesirable due to consequential increase in cost and reduction in throughput.
A number of strategies have been employed in order to enhance the positional accuracy (i.e., alignment) of substrates throughout the processing system. For example, a transfer chamber may be equipped with groups of four sensors adjacent the entry of each load lock and process chamber in a sensor arrangement such that the sensors may simultaneously detect the presence of the four corners of a rectangular glass panel for sensing its alignment prior to the robot transferring the substrate into the chamber. Thus, the four sensors are arranged in the base of the transfer chamber at spaced-apart locations such that all four sensors are simultaneously positioned below the four corners of the stationary substrate. Such a disperse arrangement of sensors in front of each of the chambers requires a large number of sensors positioned at many locations across the base of the transfer chamber. Various arrangements of sensors disposed across the base of the transfer chamber have been proposed.
Although conventional sensor arrangements perform satisfactorily, in operation there are several inherent limitations associated with providing these arrangements of sensors. In practice, because the sensors detect the alignment of a single substrate at a time, the transfer chamber may handle/manage only one substrate at a time due to the disperse arrangement of sensors across the base of the transfer chamber. Thus the transfer chamber robot is effectively limited to a single-arm robot which results in reduced throughput of the processing system. Another limitation, which also contributes to a reduced throughput of the processing system, is that the substrate is stationary when positioned over the four sensors during the sensing of its alignment. Still another limitation is at least four sensors are required to sense the alignment of a single substrate. Finally, another limitation is that the four sensors detect substrate defects (e.g., a substrate chip) only at the corners of the substrate.
With the apparatus and method of the present invention, the relatively simple arrangement and few number of sensors required to detect the misalignment and/or breakage of a substrate make the present invention easy to implement with relatively low cost.